This is a terrible argument. Here’s an example that will hopefully make this clear. Let’s say I have a friend named Steve. Steve is a murderer. And murder, unlike terrorism, is a huge problem, right? Well, it turns out that murder by Steve is a tiny problem. Steve only murders, let’s say, 10 people a year. That’s less than the number of people who die every year in parachuting accidents! So murder-by-Steve isn’t worth worrying about, just like terrorism.

Right?

Let’s call this general move conceptual gerrymandering. I can make a problem look either big or small by drawing either a big or small conceptual boundary around it, then identifying my problem with the conceptual boundary I’ve drawn.

What’s the #1 cause of death in the US today? The standard answer is heart disease, which makes heart disease sound like a really big problem. Okay, but what actually is heart disease, really? Mayo Clinic says:

The term “heart disease” is often used interchangeably with the term “cardiovascular disease.” Cardiovascular disease generally refers to conditions that involve narrowed or blocked blood vessels that can lead to a heart attack, chest pain (angina) or stroke. Other heart conditions, such as those that affect your heart’s muscle, valves or rhythm, also are considered forms of heart disease.

In other words, heart disease is not one disease, it’s a whole bunch of diseases; in fact it’s a whole bunch of categories of diseases. What makes this a single cause of death, rather than four, or however many different named heart diseases there are? Why don’t we just lump all the diseases together and call the real #1 cause of death “disease,” which surely must be a strictly bigger problem than merely heart disease?

The real answer to the question “what’s the #1 cause of death in the US today?” is that causes of death are arbitrary conceptual boundaries that people (apparently the World Health Organization) drew at some point for reasons, and those reasons might not have anything to do with the reason you’re asking this question. The WHO might choose to draw the boundaries of causes of death the way they do to track various health trends over time (for example, it would be interesting and relevant if the rate at which Americans died of heart disease changed substantially in either direction), but there are lots of other reasons you might want to know something about causes of death, including but not limited to

and for these applications it might make sense to use a totally different set of conceptual boundaries.

Back to terrorism. One of the points of the Parable of Steve is that you can make terrorism look small by gerrymandering a tiny conceptual boundary around it, even though a larger conceptual boundary might be more natural. As a somewhat silly example, why isn’t terrorism considered a form of homicide? That would make it look a lot bigger: homicide is cause of death #17, for what that’s worth.

We can also extract from the Parable of Steve some pointers towards what a good argument for or against worrying about terrorism might look like. For example, sometimes the relevant metric isn’t how many deaths something causes, it’s how easy it would be to prevent those deaths. Steve the murderer doesn’t kill many people, but preventing the people he would kill from dying is as easy as locking Steve up in jail, which is a lot easier than, say, curing even a single form of heart disease, or preventing heat waves.

It’s also relevant that Steve is a person, and we can interact socially with people (unlike with lightning strikes, heat waves, guns…). Arresting Steve has social effects other than just preventing Steve’s victims from dying: it

sends a message to other would-be murderers that murdering will not be tolerated, and might help prevent them from murdering too, and

sends a message to would-be murder victims that they will be kept safe.

This point of view naturally encourages drawing a conceptual boundary around Steve to include all murderers, not just Steve. We may even want to draw a larger conceptual boundary around Steve that includes all violent crime, or even all crime.

It’s also relevant that Steve’s victims don’t get much warning that they’re going to die. Many causes of death kill you slowly, cancer particularly, and you can plan for the future accordingly, for example by writing a will. But Steve’s victims die suddenly and unpredictably, and knowing that you live in the same area as Steve the murderer who’s not in jail makes your life less predictable in a pretty awful way.

Analogously, there are several mechanisms by which terrorism could be a serious problem worth doing something about despite not killing very many people (although I don’t feel strongly about this, and it’s probablynot):

It might be easy to prevent terrorism, for example by being “hard on terror.”

Being hard on terror might have beneficial social effects, by sending a message to other would-be terrorists that their behavior won’t be tolerated, and by sending a message to would-be terror victims that they will be kept safe.

Preventing terrorism might make life more predictable in an important way.

These arguments might seem a little wishy-washy. To supplement them, here is a Second Parable of Steve. This time he’s not a murderer, but every once in awhile, when he comes over to my house, he steals some of my forks.

Is this a big problem? In some sense, no. Forks cost peanuts. If I were just losing forks every once in awhile, I would think about this problem approximately never, except maybe I would buy forks a little more often.

But am I going to do something about it? Absolutely. I’m not going to tolerate that kind of shit from Steve, or anyone else, and do you know why?

Because I don’t want to adopt the policy of having friends who feel like they can hurt me like that. This policy has social effects. If I’m seen to have it, I run the risk of acquiring a lot of friends who slowly bleed all of the joy out of my life, one fork (or whatever) at a time. Even if Steve’s the only friend of mine who does stuff like that, if he sees me letting him steal his forks, he might get braver and do something worse in the future.

So the problem is bigger than a naive description of it makes it seem. It is not about Steve stealing my forks. It is about letting people like Steve do things to me as bad as stealing my forks, which is a very different and potentially much larger conceptual boundary.